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Emerald ash borer

The emerald ash borer was first detected in North America in 2002, but probably arrived on this continent at least a decade earlier. Native to Asia, the beetle has proven to be highly destructive in its new range. Since its arrival, it has killed tens of millions of ash trees and continues to spread into new areas, with considerable economic and ecological impacts.

Canadian Forest Service (CFS) scientists estimate that costs for treatment, removal and replacement of trees affected by emerald ash borer in Canadian municipalities may reach $2 billion over a 30-year period. Also expected to be significant are the ecological impacts of ash tree mortality on aquatic organisms, birds and understory vegetation, currently under study.

Status

Emerald ash borer in Canada was first detected in 2002, in Windsor, Ontario. By 2005, it had spread into Essex and Lambton counties and the municipalities of Chatham-Kent and Dutton/Dunwich. In 2006, it was detected in London, Ontario; and in 2007, as far east as Toronto. The insect has continued to spread in that province since, with infestations appearing as far north as Sault Ste. Marie and as far east as Ottawa and Prescott-Russell and Leeds-Grenville counties. In 2013, the beetle was detected in Frontenac County, Simcoe County, Peterborough County, the District of Algoma, and Manitoulin Island.

The presence of emerald ash borer in Quebec’s Montérégie area was confirmed by the Canadian Food Inspection Agency (CFIA) in 2008. Infestation in Montreal and the Gatineau area were detected in 2011; Longueuil in 2012; and Terrebonne in 2013.

In 2014, CFIA consolidated the regulated areas within Ontario and Quebec into one larger regulated area.

Influencing factors

In North America, the emerald ash borer has few effective natural enemies, and native ashes have limited resistance to attack. Surveys have shown that the emerald ash borer damages and kills trees in stands within one to four years of infestation.

Typically, within six years of an infestation arriving in a woodlot, more than 99% of the ash trees have been killed. This extensive mortality increases the likelihood of invasion of forests by invasive plants, and poses a significant challenge to affected urban centres.

Outlook

The area infested by emerald ash borer is expected to continue to expand, mostly through human movement of infested material such as firewood. Extensive areas with a large proportion of native ash trees have yet to become infested; the impact is therefore predicted to continue to increase as these forested areas are colonized by the emerald ash borer.

CFS researchers are investigating the spread (both natural and assisted) and impact of emerald ash borer in these more heavily forested landscapes. In addition, cities throughout central and western Canada often have a high proportion of ash in their urban tree inventories, and will be significantly affected if or when emerald ash borer arrives in those locations.

Challenges and research

It is difficult to detect the emerald ash borer at low population levels. The visual survey method—looking for signs and symptoms of attacks—is often used to survey for the insect. However, in the early stages of an infestation, signs and symptoms are not readily apparent. This makes infestations hard to notice until numerous heavily infested dead and dying ash trees become evident.

Progress has been made, however. The United States Department of Agriculture scientists have developed a green prism trap system for detecting emerald ash borer infestations, and CFS researchers were involved in the development of a green-leaf volatile lure as bait for the traps.

Used by the CFIA since 2010, this combination has resulted in the detection of new infestations outside of the regulated areas. Traps are also now deployed by the Province of Ontario and numerous municipalities to supplement the CFIA’s surveys.

Other research underway with this insect:

Female-produced pheromone

CFS researchers have demonstrated the attraction of male emerald ash borers to a female-produced pheromone. Use of the pheromone increases both trap captures and trap detection rates. It is now available commercially as a lure that can be applied in combination with the green-leaf volatile lure on the green prism traps.

As well, CFS researchers are testing a synthetic version of this pheromone, which could represent a more-cost effective option as a trap lure. They are also investigating the use of the pheromone to disorient males and thereby reduce successful mating. This research involves scientists at Great Lakes Forestry Centre, Atlantic Forestry Centre, and Laurentian Forestry Centre.

Branch sampling

CFS researchers in Sault Ste. Marie have developed a novel survey method that involves sampling branches pruned from the crown of host trees. This method, which yields a high rate of detection of asymptomatic infestation, is currently being used by many municipalities and the provincial forest health monitoring group. It is especially effective when carried out in follow-up to positive results of trapping surveys, helping pinpoint which trees are infested and to what extent.

Biological control

The potential for long-term biological control of emerald ash borer is being studied. Some natural enemies, such as native parasitoids (insect parasites that kill their hosts) and insect pathogenic fungi, may help reduce emerald ash borer populations. CFS researchers are studying the levels of mortality these parasitoids and pathogens cause, as well as methods for increasing or augmenting their populations.

CFS researchers in Sault Ste. Marie, in collaboration with Carleton University, are investigating patterns of forest habitat loss and fragmentation at the landscape scale to determine how these factors might influence native natural enemy populations to emerald ash borer.

Researchers in the U.S. are continuing to study parasitoids imported from China to battle the insect as part of a biological control program. Numerous releases of three species of imported parasitoids have taken place in infested areas throughout the northeastern U.S., and populations have established at several release locations.

Systemic insecticide

CFS researchers, in partnership with BioForest Technologies Inc., developed TreeAzin™, a systemic insecticide to protect individual high-value ash trees and trees in isolated infestations. TreeAzin™ is formulated from an oil derived from seeds of the neem tree (a member of the mahogany family), and was granted full registration in 2012. Now commercially available, TreeAzin™ is being used by numerous municipalities and tree care companies as one component of their emerald ash borer management strategy.

Pathways and patterns of spread

Costs and benefits of management options

CFS researchers are developing models for estimating the economic costs and benefits of various management options.

Overwintering physiology

CFS researchers, in collaboration with scientists from the universities of Western Ontario and Waterloo, are working to understand the overwintering physiology of emerald ash borer, and its potential survival and distribution in Canada’s cold winter climate. Prepupae, the overwintering stage of emerald ash borer, can withstand average minimum temperatures of –30°C by employing antifreeze compounds.

Regulatory practices

CFS scientific staff, through the National Emerald Ash Borer Scientific Committee, are providing proactive support to the CFIA in establishing sound regulatory practices based on the best scientific knowledge available.

Up-to-date scientific information

Because human-assisted movement is an important risk factor in the spread of emerald ash borer, CFS technology transfer and scientific staff are active in providing the media with up-to-date scientific information and keeping both general public and groups—including stakeholders, foresters and municipal forest technicians—well informed about the insect’s threat, its patterns of spread, and methods of control.